Time Division Multiplexing for Light Field Display

The present disclosure relates to light field display technology and more specifically, to methods of time division multiplexing (TDM) and optical components for holographic displays. The present disclosure particularly relates to a system and method for multiplexing a multiple view, light field display, resulting in high angular resolution and a wide field of view (FoV).

Light field displays provide multiple views, allowing a user to receive a separate view in each eye. A light field display without eye tracking offers significant advantages in terms of user experience, accessibility, and practicality. It provides a simpler and more comfortable viewing experience, free from the intrusiveness and discomfort that eye tracking hardware and software can introduce. Such displays are more accessible to a wider audience, eliminating the need for specific technological proficiency or physical accommodations. Additionally, they offer enhanced reliability and consistency by avoiding the inaccuracies that can plague eye tracking systems due to lighting, movement, or calibration issues. The absence of eye tracking also reduces the overall cost and complexity, making the technology more affordable and easier to integrate into various applications. Furthermore, these displays are straightforward to use, requiring no additional setup or calibration, allowing users to interact with them immediately. Overall, light field displays without eye tracking provide a more intuitive, accessible, and reliable solution for delivering immersive visual experiences.

While current displays in this category provide an interesting viewing experience, a captivating light field display requires a high pixel density, low angular separation between views, and a large viewing angle. For a high-quality viewing experience, it is desired that a user experiences smooth transitions between viewing zones while maintaining an independent and perceivable view from the adjacent views. Three-dimensional light field displays allow the viewer to gain a broader perspective on the image they are viewing. Some three-dimensional displays use polarized light and require the viewer to wear specialized glasses. Others produce an image that provides some parallax in a single dimension.

High resolution light field displays require small scale (nano- or micro-scale) pixels. When used in a display, a reduced pixel size allows the system to output a greater number of light beams, allowing the generation of higher angular resolution displays with improved spatial resolution of multi-dimensional objects. Fabrication of nano- or micro-scale pixels is new and challenging. Additionally, to produce the increased number of light-field display views required to allow a viewer located at any viewing position to simultaneously receive multiple views, the light emitted by each pixel must be directionally controlled with a high degree of precision and accuracy.

U.S. Pat. No. 10,244,230 to Haas et al. describes a directional pixel for a high-angular resolution, wide field of view, multiple view display. The design teaches a directional pixel comprising a substrate, one or more pixel driving circuits, one or more nano- or micro-scale subpixels, and one or more directional optical guiding surfaces, wherein each of said one or more subpixels is comprised of a light emitting device emitting a light beam and an optical microcavity housing said light emitting device. The optical microcavity is comprised of a plurality of reflective surfaces to specifically manipulate and tune said light beam, wherein one or more of said reflective surfaces is a light propagating reflective surface which propagates said light beam out of said microcavity, and said light propagating reflective surface is connected to said one or more directional optical guiding surfaces to direct said light beam at a specific angle.

An alternative to generating the multiple views required for a high-quality light field display at the pixel may include implementation of a multiplexing technique. Multiplexing allows for the transmission of several signals over a common channel. One example is time division multiplexing (TDM), which is a technique wherein a complete signal is transmitted over a common channel while occupying separate time slots. In TDM, a time division technique is performed by synchronizing switches at each end of the transmission line so that each signal appears on the line only a fraction of time in an alternating pattern to produce a multiplexed data signal.

United States patent application publication number US2022/0179193 to Bevensee et al. describes an energy directing system with one or more energy sources and a plurality of energy directing surfaces configured to direct incident energy along a plurality of energy propagation paths in a time-sequential manner. Bevensee et al. teaches that modules having an energy source (such as a laser) and an energy-deflecting surface (such as a micromirror) can be used to project many 4D propagation paths per interval of time.

The density of views produced by a light field display may be increased through the dynamic manipulation of the polarization state of light combined with polarization sensitive optical components enabling TDM of light field content. Polarizing optical components, which include but are not limited to polarizers, liquid crystal devices, phase retarders, and Pancharatnam-Berry optical elements, are examples of optical components that can manipulate the polarization state of light. An optical stack of these devices can not only control the final polarization state of transmitted light, but also the transmission and directivity of the stack, or how much light is being transmitted and in what direction.

In another example, United States patent application publication number US2022/0187529 to El-Ghoroury et al. describes a method and apparatus for achieving selective polarization states of emitted visible or other light in a stacked multicolor emissive display device by utilizing nonpolar, semipolar, or strained c-plane crystallographic planes of semiconductor materials for light emitting structures within an electronic emissive display device. However, exploiting light polarization heavily impacts system efficiency as, in addition to the expense of implementing multiple polarization sensitive optical components into a display, the initial polarization of light from an organic light emitting diode light source discards 50% of the light produced.

This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.

It is an object of the present invention to provide a device, optical system, and method of creating a time division multiplexing (TDM) light field display. It is another object to provide a TDM light field display that uses light polarization components and techniques to produce high resolution pixel density in a light field.

In an aspect there is provided a device for displaying a time multiplexed light field comprising: a pixel array; a time division multiplexing system; and a directional optical element.

In an embodiment, the time division multiplexing system comprises a polarization sensitive optical system and a polarization sensitive beam deflector.

In another embodiment, the polarization sensitive optical system comprises: a circular polarizer comprising a quarter wave plate for receiving incoming light and providing a circularly polarized light beam; a circular polarization switcher comprising a switchable half wave plate; and a control system for controlling current to the circular polarization switcher.

In another embodiment, the circular polarizer further comprises a linear polarizer before the quarter waveplate.

In another embodiment, the linear polarizer comprises an absorptive polarizer, beam-splitting polarizer, linear polarizing film, dichroic polarizer, wire grid polarizers, birefringent polarizer, or dichroic polymer thin film polarizer.

In another embodiment, the circular polarization switcher is a switchable liquid crystal half wave plate.

In another embodiment, the circular polarization switcher comprises a liquid crystal cell comprising: a substrate; a first electrode; an alignment layer; a liquid crystal material; and a second electrode.

In another embodiment, the circular polarization switcher comprises a birefringent material selected from one of liquid crystals, quartz, and magnesium fluoride.

In another embodiment, the circular polarization switcher comprises a switchable liquid crystal half wave plate comprising a liquid crystal material comprising one or more of a birefringent material and a thermotropic material with a rod-like molecular shape.

In another embodiment, the polarization sensitive beam deflector comprises a birefringent material element, liquid crystal device, polarizing beam splitter, electro-optic or acousto-optic device, chromatic beam deflector, achromatic beam deflector, or Pancharatnam-Berry optical element.

In another embodiment, the directional optical element comprises one or more of a lens, lens array, mirror, prism, diffraction grating, waveguide, optical fiber, beam splitter, metasurface, and metalens.

In another embodiment, the linear polarizer is designed for maximum efficiency versus extinction ratio, p.

In another aspect there is provided a method for creating a time multiplexed light field comprising: receiving a light beam from a pixel array; deflecting the light beam by a deflection angle; and directing the deflected light beam at a directional optical element to generate a light field.

In an embodiment, the method further comprises transforming the light beam received from the pixel array into a linearly polarized light beam.

In another embodiment, the method further comprises transforming the linearly polarized light beam into a circularly polarized light beam having a rotational handedness.

In another embodiment, the method further comprises, at a circular polarization switcher, reversing the rotational handedness of the circularly polarized light beam or retaining the rotational handedness of the circularly polarized light beam.

In another embodiment, the circularly polarized light beam is deflected and directed to the directional optical element to generate the light field.

In another embodiment, the deflection angle is based on a rotational handedness of the circularly polarized light beam.

In another embodiment, the deflected light beam shifts a virtual pixel position by a factor of one or more of one half of an angular pitch ((/) and one quarter of the angular pitch ((/) of pixels in the pixel array.

In another embodiment, the circular polarization switcher is a switchable liquid crystal half wave plate, and wherein retaining the rotational handedness comprises applying a threshold voltage to the switchable liquid crystal half wave plate sufficient to retain the handedness of the circularly polarized light beam.

In another embodiment, deflecting the circularly polarized light beam angle comprises receiving the circularly polarized light beam at a polarization sensitive beam deflector, the polarization sensitive beam deflector configured to deflect the circularly polarized light beam of a first handedness by a first angle in a first direction and to deflect the circularly polarized light beam of the reversed handedness by a second angle in a second direction.

In another embodiment, the light beam is received from a Light Emitting Diode (LED), projector device, Organic Light Emitting Diode (OLED), active-matrix organic light emitting diode (AMOLED) array, or electroluminescent (EL) device.

In another aspect there is provided a time division multiplexing (TDM) optical system comprising: a pixel array comprising a plurality of pixels, each pixel in the pixel array generating a light beam; a circular polarizer comprising: a linear polarizer for receiving the light beam and providing a linearly polarized light beam; and a quarter wave plate for receiving the linearly polarized light beam and providing a circularly polarized light beam; a circular polarization switcher for receiving the circularly polarized light beam and alternately switching between a first circularly polarized light beam of a first handedness and a second circularly polarized light beam of a second handedness, the circular polarization switcher connected to a control system to control current to the circular polarization switcher; a polarization sensitive beam deflector configured to deflect the circularly polarized light based on its handedness; and a directional optical element configured to receive the deflected circularly polarized light from the polarization sensitive beam deflector and generate a light field.

In an embodiment, the pixel array is in an active-matrix organic light emitting diode (AMOLED) array.

In another embodiment, the circular polarization switcher alternates between the circularly polarized light beam of the first handedness and the second circularly polarized light beam of the second handedness at least every 30 Hz.

In another embodiment, the polarization sensitive beam deflector comprises a birefringent material element, liquid crystal device, polarizing beam splitter, electro-optic or acousto-optic device, chromatic beam deflector, achromatic beam deflector, or Pancharatnam-Berry optical element.

In another embodiment, the polarization sensitive beam deflector is a controllable polarization sensitive beam deflector that can further control the deflection angle of the emitted light beam.

In another embodiment, the controllable polarization sensitive beam deflector is a controllable Pancharatnam-Berry (PB) beam deflector.

In another embodiment, the polarization sensitive beam deflector is connected to an electrical current source.

In another embodiment, the controllable polarization sensitive beam deflector is connected to an electrical current source.

In another embodiment, the system further comprises a linear polarization switcher configured to receive and alter an orthogonal orientation of the linearly polarized light beam.

In another embodiment, the linear polarization switcher is an Electro-Optic Modulator (EOM), Liquid Crystal Device (LCDs), Acousto-Optic Modulator (AOM), Magneto-Optic Modulator, Mechanical Polarization Switch, or Digital Polarization Rotator.

In another embodiment, the linear polarization switcher switches a plane of linearly polarized light by +/−45°.

In another aspect there is provided a time division multiplexing (TDM) optical system comprising: a linear polarization switcher connected to a control system configured to receive a linearly polarized light beam and alternately switch between the linearly polarized light beam between a first orthogonal direction and a second orthogonal direction; a quarter wave plate for receiving the linearly polarized light beam and providing a circularly polarized light beam; a circular polarization switcher for receiving the circularly polarized light beam and alternately switching between a first circularly polarized light beam of a first handedness and a second circularly polarized light beam of a second handedness, the circular polarization switcher connected to a control system to control current to the circular polarization switcher; a polarization sensitive beam deflector configured to deflect the circularly polarized light based on its handedness; and a directional optical element configured to receive the deflected circularly polarized light from the polarization sensitive beam deflector and generate a light field.

In another aspect there is provided a device for light beam multiplexing comprising: a circular polarizer comprising a quarter wave plate for receiving incoming light and providing a circularly polarized light beam; a circular polarization switcher comprising a switchable half wave plate; a control system for controlling current to the circular polarization switcher; a polarization sensitive beam deflector; and a directional optical element.

In another aspect there is provided a method for creating a multiplexed light field comprising: receiving a light beam from a pixel array; transforming the light beam into a linearly polarized light beam; transforming the linearly polarized light beam into a circularly polarized light beam having a rotational handedness; receiving the circularly polarized light beam at a circular polarization switcher, and either reversing the rotational handedness of the circularly polarized light beam or retaining the rotational handedness of the circularly polarized light beam; deflecting the circularly polarized light beam at a deflection angle based on the rotational handedness of the circularly polarized light beam; and directing the circularly polarized light beam at a directional optical element to generate a light field.

In another aspect there is provided a time division multiplexing (TDM) optical system comprising: a pixel array comprising a plurality of pixels, each pixel in the pixel array generating a light beam; a circular polarizer comprising: a linear polarizer for receiving the light beam and providing a linearly polarized light beam; and a quarter wave plate for receiving the linearly polarized light beam and providing a circularly polarized light beam; a circular polarization switcher for receiving the circularly polarized light beam light beam and alternately switching between a circularly polarized light beam of a first handedness and a second circularly polarized light beam of a second handedness, the circular polarization switcher connected to a control system to control current to the circular polarization switcher; a polarization sensitive beam deflector configured to deflect the circularly polarized light based on its handedness; and a polarization insensitive directional optical element configured to receive the deflected circularly polarized light from the polarization sensitive beam deflector and generate a light field.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

The use of the word “a” or “an” when used herein in conjunction with the term “comprising” may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one” and “one or more than one.”